The invention relates to a tensioning device for gear belts, chains (toothed belts, chains) and the like. Preferred embodiments of the invention relate to such tensioning devices for a camshaft drive of an internal combustion engine. In such tensioning devices, a tension pulley or roller is provided which cooperates directly with a gear or toothed belt. The distance of the tension pulley or roller from an adjustable support arranged at the internal combustion engine housing is influenced by a heat-depending control element to thereby control the tension of the gear or belt.
A tensioning device for belts, chains or the like is known (DT-PS No. 856,980) which is constructed with a tension roller arranged on a lever swingable about an axis, and which is pressed with tension against the belt by, for example, a spring. As a result of the spring characteristic, an exact matching to the various temperature-dependent operating ranges of the internal combustion engine, is not possible in this case.
For avoiding this disadvantage, a tensioning device is known through an older patent application (DOS 2,535,676), in which a tension roller is arranged at an axial-adjustable housing which is supported at an adjustable abutment whereby the tensioning device includes elastic blocks arranged in the housing and between which a swing-lever is arranged so as to cooperate with a heat-dependent control element. With this arrangement, however a relative high vibration of the elastic block has proven to be especially disadvantageous since, as a result of these vibrations, a flutter-free operation of, for example, the toothed belt during all rotation ranges of the internal combustion engine was not attained and the operating noise of the toothed belt was increased considerably and the life of the belt was reduced. In addition, the change in length of the control element, constructed with bimetal, was extensively compensated through the elastic blocks so that thereby, for the belt tension itself, not enough attention was given to the variable heat conditions at the internal combustion engine to the required extent.
It is an object of the invention to create a tensioning device for toothed or gear belts, chains or the like, especially for a camshaft drive of an internal combustion engine, through which a uniform gear belt tension is assured in all occurring stationary and unstationary operating conditions of the internal combustion engine.
Inventively, this is solved with a tensioning device of the type mentioned at the outset wherein the heat-dependent control element is constructed by a number of bimetal-disk springs which are stacked together in alternating directions.
The advantages obtained with the inventive tensioning device consist especially therein, that all criteria for assuring satisfactory operation of, for example, a belt, are fulfilled. The required gear-belt tension is maintained between the maintenance intervals and is the same with all occurring stationary and unstationary operating conditions. Further, a skipping of the gear belt during return rotation of the internal combustion engine is safely assured and a flutter-free operation of the gear belt is assured in a sufficient measure at every rotative speed.
These and other objects, features and advantages of the present invention will become more apparent from the following description when taken in connection with the accompanying drawings, which show, for purposes of illustration only, a single embodiment in accordance with the present invention.